This invention relates to an automatic control system of an earth-moving equipment, and more particularly, to a control system of the blade of a bulldozer.
When using a bulldozer in an earth-moving work it is necessary to maintain its blade at a desired cutting angle with respect to the ground surface so as to level the ground as desired without overloading the bulldozer. According to one proposed system, a reference plane is established by using a laser beam or the like and the blade is controlled to follow the reference plane.
According to such a prior art system, however, when an overload condition is encountered, a phenomenon which is termed by experts as stall phenomenon occurs in which although the engine of the bulldozer is operating no torque is transmitted to the load side, thus interrupting the operation of the machine. Accordingly, it is necessary to avoid an excessively large cutting angle of the blade that causes overloading. On the other hand, if the cutting angle is too small, the working effeciency of the bulldozer will be low.
Another problem encountered in the operation of a bulldozer involves the cutting depth of the blade. If the cutting depth is too large this will also cause overloading. An ON-OFF control system has been used to control the cutting depth of the blade. In order to stabilize such a control system it has been the practice to increase the width of the insensitive zone of the control system that determines the accuracy of the earth moving work or to decrease the operating speed of a hydraulic pressure cylinder that drives the blade. To increase the accuracy of the earth moving work or to level the ground at a high degree of flatness it is necessary to sufficiently decrease the operating speed of the hydraulic pressure cylinder and hence the running speed of the earth-moving equipment, otherwise a stable control system could not be obtained. On the other hand where rough levelling is permissible, or where a high degree of accuracy is not required, the width of the insensible zone may be increased. Under these conditions it is possible to increase the operating speed of the hydraulic pressure cylinder and hence the running speed of the equipment.